Previous methods for making high precision glass tubing employ the well-known redraw technique in which a close tolerance redraw blank tube is drawn down to a smaller size on a mandrel to make such articles as glass ferrules. See for instance U.S. Pat. Nos. 4,850,670, 5,295,213, 5,314,517, 6,098,428, and 6,810,691.
In all of the various redraw processes, the dimensional characteristics of the tubular starting blanks substantially control all of the final dimensions of the redrawn tubing. Such things as roundness, concentricity of inner bore to outer diameter and the ratio of inner bore size to the outer diameter can not be changed during redraw, and as a consequence, the greatest proportion of the cost to make redraw tubing lies in the original blank preparation costs and the very inefficient batch type non-continuous redraw operation.
My previous method of making high precision glass tubing, described in U.S. Pat. No. 3,401,028, employs bulky and expensive equipment and generally is incapable of forming glass tubing having the high precision required for many modern applications, such as the manufacture of glass ferrules or connectors for optical fibers. These applications may require precise inside and outside dimensions, wall thickness, roundness, and concentricity, all measured in nanometers, for example one hundred nanometers or less, sometimes ten nanometers or less.
Other methods of forming glass tubing are shown in U.S. Pat. Nos. 4,350,513 and 4,372,771.
The patents mentioned above are hereby incorporated by reference.